<!DOCTYPE html>
<html>
    <head>
        <meta charset='utf-8' />
        <style>     
           img{
               opacity:0.5;
               transition:opacity 1s ease-in;
           }
           
           img:hover{
               opacity:1;
           }
        </style>
    </head>
    <body>
        <img src='./images/1.jpg' title='小萝莉和她宠物狗'  />
    </body>
</html>